Several methods and devices are in current use for measuring the density of drilling fluids used to drill oil and gas wells. All of these devices and methods measure only the density of fluids in surface facilities and none incorporates the capability of vertical height measurement of a fluid column in a riser.
In the method of the invention measurements of the drilling fluid density may be made with the drilling fluid in either a static or dynamic condition. Also, the height of the fluid column in the riser above a known reference level is measurable when the density of the fluid is known.
The invention has several advantages over existing methods and devices used to measure drilling fluid densities. The drilling fluid density measurements are made using a length of well bore annular drilling fluid column in either a static or dynamic state and prior to separation of any drilled solids or gas. In this manner a more realistic measurement of the density of the drilling fluid returns is provided. With the measured density of the drilling fluid, the height of the drilling fluid column above a reference point is continuously measured. Such capability can be used to locate the level of the drilling fluid column in the event of complete loss of circulation and to measure the volume of fluid needed to fill the hole when "pulling" the drill string (trip out). Marine drilling may in the future require airlift of the returns drilling fluid to prevent loss of circulation. When airlift is required, monitoring of the total hydrostatic head in the marine riser will be essential for well control. The present invention provides such capability. Any appreciable column of formation gas entering the well bore and rising to a point above the reference point in the riser will result in a reduction in the average density of the measured fluid column and therefore can be detected by the method of the present invention.